1. Field
This art is related to an electronic circuit device having a power-gating function.
2. Description of the Related Art
One of the functions to reduce power consumption of semiconductor integrated circuits used for electronic devices is a power-gating function. A power-gating function stops supplying electronic power to a domain of an internal circuit that is in a standby mode. In this way, power consumption can be minimized when the domain is in a standby mode, thus increasing the continuous operating time of electronic devices.
A high threshold transistor can be used for a switch for shutting off the power. A high threshold transistor has an excellent ratio of driving an electrical current when a switch is on to a small leakage current when the switch is off. In order to drive such a high threshold transistor, Japanese Patent Application Laid-open No. 6-29834, for example, describes a switching control unit that controls a switching operation using a second power supply voltage higher than a first power supply voltage used for an internal circuit.
In widely used large-scale integrations (LSIs), the power supply voltage for an I/O circuit is higher than that for an internal circuit. Accordingly, a power supply of an I/O circuit is used for a power supply of the switching control unit. However, in such a case, simultaneous switching noise caused by simultaneous switching of the I/O circuit (known as simultaneous switching output (SSO) noise) is transferred to the switching control unit, which is problematic. By using the second power supply of the I/O circuit for the power supply of the switching control unit, SSO noise caused in the I/O circuit affects superposed on a switch control signal for controlling a switching operation of the high threshold transistor. Therefore, the switching operation of the high threshold transistor becomes unstable. As a result, the operation of the internal circuit operating with the first power supply supplied via the high threshold transistor becomes unstable.